The invention relates to a method for controlling the operation of an arrangement of at least two electric machines which are coupled for movement with different wheels of the motor vehicle and are connected to a battery, which battery provides an actual minimum and an actual maximum limiting current for the electric machine provides, wherein desired torques for the electric machines are provided by a drive control logic. In addition, the invention relates to a motor vehicle.
Drive arrangements have been proposed in the technical field of motor vehicles for both all-electric vehicles and hybrid vehicles, which assign an electric machine to at least two wheels of an axle of the motor vehicle, in particular to all four wheels, so that the wheels of the motor vehicle arranged on the same axle can be driven independently. Intentionally accelerating individual wheels is useful when operating some driver assistance systems, such as anti-lock braking systems, anti-slip systems, electronic stability control systems, vehicle dynamics systems and the like. In particular, however, it is also conceivable to realize a steering operation by an appropriate activation of the electric machine. For example, the drive torque can be reduced on one side by a predetermined value and increased on the other side by a predetermined value so as to produce a steering action. Such an approach is known in the art as electric torque vectoring, eTV, and distribution of the driving dynamics in the transverse direction.
Such a motor vehicle, wherein a corresponding electric machine is associated with the drive wheels of an axle, is known, for example, from DE 10 2007 056 301 A1. Therein, the drive wheels of the axle can be independently driven or independently regeneratively braked. The electric machines are used for generating specific drive torques or braking torques whereby an actively controllable transverse torque distribution can be implemented at the first axle for stabilizing the vehicle in critical situations.
However, problems always occur with electric torque vectoring in such an environment, when the battery used to drive the electric machines, especially a high-voltage battery, is full or empty, i.e. when the battery assumes particular states of charge where the charge or discharge current is severely limited. In this situation, an excessive charge current may occur when the battery is, for example, full, posing a risk for the battery. A similar problem may occur when the battery is empty or almost empty, when an excessive energy demand exists in the system. As a result, the driving dynamics cannot be distributed in the transverse direction (electric torque vectoring) when the battery is either full or empty. In hybrid vehicles, such problem preventing the distribution of the driving dynamics in the transverse direction may also occur when the battery is very cold or very hot, i.e. when the battery temperature falls below or exceeds certain limiting temperatures, since the charge or discharge current is then also very limited. This problem does not occur in all-electric vehicles, because these are unable to drive with a cold battery.
Electric machines associated with the same axle of a motor vehicle are usually controlled by a drive controller by identifying desired torques to be generated at the electric machines. As part of controlling the electric machines, a current is then “predicted” (current forecast) for the electric machines so as to realize these desired torques. It may be possible in a simple embodiment, whenever a battery driving an electric machine is full, to predict the actual current of the opposite electric machine as an additional generator current through appropriate communication in the drive system, whereas when the battery is empty and the electric machine is in regeneration mode, the generated actual current of the opposite electric machine can be predicted as an additional motor current. The actual currents are thus shifted so that the control delay caused by the communication is always on the non-critical side of the battery current. However, there is the serious disadvantage in that control delays occur as a result of the time taken up by the bus communication, which can lead to unintended effects and to a reduction of the comfort.